rpi usb power

kookyflap · Tue Mar 03, 2015 6:51 am

I want to power a laser using the raspberry pi, but the power output of the USB port is only 100mA, is there a way to increase this number or am i better off using the gpio?
p.s. I read there is a way to increase the amps by connecting the output of the polyfuse to the usb power, is this safe?

rpdom · Tue Mar 03, 2015 6:57 am

Which model Pi do you have?

The original Model B had 140mA polyfuses on each USB port to limit the current. The later B, Model A and the A+ don't have those fuses, but the total current is still limited by the main polyfuse.

On the B+ and Pi2, the default current is limited to 600mA combined total for the four USB ports. That can be increased to 1200mA by putting max_usb_current=1 in /boot/config.txt.

kookyflap · Tue Mar 03, 2015 7:00 am

i have the a+.

rpdom · Tue Mar 03, 2015 7:04 am

You should be able to take 500mA from the USB port on an A+. AFAIK there isn't a limiter on an A+, other than the main polyfuse.

kookyflap · Tue Mar 03, 2015 7:06 am

so does that mean that every usb port would only have 150Ma? Or would it mean that it would just be divided every time you plug something in?
P.S. i am using a 4 slot not powered usb hub for my a+.

kookyflap · Tue Mar 03, 2015 7:07 am

my bad, i posted the last comment before i read your answer.

kookyflap · Tue Mar 03, 2015 7:10 am

on an unrelated note, You seem to know a lot about the rpi, could you answer this question? sorry if it is blatantly obvious, or ignorant.
I have recently acquired a pi 2 and wanted to make it thinner.
Is there any way to remove the Ethernet and USB ports, and replace the usb ports with single ones, so it is not a bulky? also leaving out the ethernet port.
Thanks

fruitoftheloom · Tue Mar 03, 2015 7:12 am

kookyflap wrote:so does that mean that every usb port would only have 150Ma? Or would it mean that it would just be divided every time you plug something in?
P.S. i am using a 4 slot not powered usb hub for my a+.

You will need a quality Mains Powered USB Hub to power the peripherals.

rpdom · Tue Mar 03, 2015 7:24 am

kookyflap wrote:I have recently acquired a pi 2 and wanted to make it thinner.
Is there any way to remove the Ethernet and USB ports, and replace the usb ports with single ones, so it is not a bulky? also leaving out the ethernet port.

Yes, you could very carefully desolder the connectors and solder in single-height ones instead. That will give you two connectors instead of four. People have said that it is easier to desolder them if you carefully cut away the casings first. I'm reasonable proficent with a soldering iron, but I wouldn't even consider attempting that on any of my Raspis.

This would, of course, invalidate the warranty.

kookyflap · Tue Mar 03, 2015 7:33 am

what about the ethernet port

rpdom · Tue Mar 03, 2015 7:35 am

That can be removed in exactly the same way, if you don't need it.

kookyflap · Tue Mar 03, 2015 7:40 am

can i power my things even if its only a laser(on a momentary switch)
a flashlight(same story)
a wifi dongle and a bluetoothfor a keyboard.
btw it is powered by 4 aa batteries and a 5 volt solar panel

kookyflap · Tue Mar 03, 2015 7:41 am

do i have to join the plugs or replace it with something?

kookyflap · Tue Mar 03, 2015 8:00 am

Sorry for my horrid typing, I was doing this whilst trying to prevent my parents from finding out that I am in fact not doing my religion homework.

davidcoton · Tue Mar 03, 2015 9:40 am

kookyflap wrote:can i power my things even if its only a laser(on a momentary switch)
a flashlight(same story)
a wifi dongle and a bluetoothfor a keyboard.
btw it is powered by 4 aa batteries and a 5 volt solar panel

do i have to join the plugs or replace it with something?

I'm not quite sure what you mean. Powering the whole system, including the RPi? Or powering the peripherals?

In any case you must get the voltage right, and you cannot directly connect two power sources together. If you don't understand what you are doing, you probably need to get someone who does understand to help and check what you are doing. Not just on this forum. If you mis-connect the batteries to another power source you can cause major damage -- fire and possibly exploding batteries.

What sort of laser, and what is it doing? Laser power runs from very little to mega. Even low power laser light is dangerous to eyesight. I am concerned if you are doing such a project and hiding it from your parents.

kookyflap · Tue Mar 03, 2015 10:04 am

Sorry, I was taken out of context. What I meant about hiding it from my parents was the distraction of the forum, not the actual electrical work.
In regards to the batteries and solar panel, I have a current regulator and a blocking diode connected to the aa batteries which are in a input/output case. It should be safe... I hope?

kookyflap · Tue Mar 03, 2015 10:20 am

I'll give you a rundown on what I am working on. Maybe you can tell me if its a good idea.
I am basically attempting to assemble a sort of survival/convenience gauntlet/watch. It will have a solar battery with a GPS/gsm module so I can dual boot into phone, raspian, and maybe an emulator.
It will have a 50 mW laser, which when focused may ignite tinder( for survival purposes) and will have a 200 lumen flashlight(just the tip with the mirror and the LED connected to the pi)I would prefer it connected to the pi for space purposes because the pi can recharge, making it r renewable during sunshine.
I will shrink wrap all exposed wires and put them inbetween the leather gauntlet and a few layers if tape.

Let me know if you want to see a parts list and a diagram of my plan.
Any feedback or help would be very much appreciated.
Don't forget to let me know about the plans.
Thanks

kookyflap · Tue Mar 03, 2015 10:37 am

Again about the batteries, they are rechargable batteries in an input/output case which has a solar panel with the diode and regulator connected to the input which comes in the form of intertwined wires, the output comes in the form of a micro USB cable. It is powering the whole pi and only the pi. It is only connected to the pi and only the pi is it connected to...the batteries and the solae panel are the only power source. They are also powering the peripherals but only through the pi. The batteries are connected to the pi through the micro USB slot.
Hopefully that cleared up some confusion .
Please let me know if I can private message you with further questions and ideas.

davidcoton · Tue Mar 03, 2015 10:53 am

Sounds OK on the power side, but I suspect AA batteries will only give 1-2 hours use from a full charge. You would need to calculate the power consumption of each part and work it all out if you are aiming at a particular run time.

I like the gadget aspect, but personally I would not use a wearable laser, particularly not with any sort of pushswitch or computer control. There is far too much risk of accidentally blinding someone -- possibly yourself. A laser device capable of starting fire needs a keyswitch to lock it off, and a cover to prevent anyone looking into it if it comes on accidentally.

Oh, and just to state the absolutely obvious for anyone reading this, NEVER look into a laser beam to see if it's working, or to see if it's safe. It isn't. Even if you think you know that it is ....

kookyflap · Tue Mar 03, 2015 9:14 pm

Would you recommend a lock , even if the laser has an adjustable driver? So I can turn it down or even off. Would you recommend a regular switch with a cover, or is a momentary switch with a cover fine?
P.s. I will upload the plans later and hopefully hear your suggestions?

davidcoton · Tue Mar 03, 2015 10:28 pm

My personal preference would be a keyswitch AND a covered pushbutton. That allows for safety under single fault conditions. Remember you will be responsible if there is an accident, so do whatever you can to design problems out. If you can think of something to go wrong and cause a problem, then think of a solution to prevent any damage.

Since this is the RPi forum, the obvious next step is to replace the physical pushbutton with a button on a small touchscreen. The equivalent to the cover is then to put the button on a screen that is not normally selected. The physical keyswitch is still necessary to guard against program or Pi hardware faults.

Again, a note for all readers. If you use a keyswitch for safety, don't leave the key in the switch when it is turned off. It should not be possible to remove the key when switched on (choose the keyswitch carefully).

kookyflap · Wed Mar 04, 2015 5:57 am

kookyflap · Thu Mar 05, 2015 5:46 am

I will post a picture of the actual watch as soon as I get all the parts.

kookyflap · Thu Mar 05, 2015 5:49 am

let me know if anyone has a suggestion regarding features or parts, before I buy the rest of the parts for the watch
.

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